1. Field of the Invention
The present invention relates to a magnetic disk storage apparatus providing a rotary head positioning mechanism and particularly to such a storage apparatus having a vibration proof structure an improved head positioning accuracy.
2. Description of the Prior Art
A head positioning mechanism is usually called a positioner or actuator and two kinds of apparatuses of linear type and rotary type mechanisms have been proposed. A rotary type head positioning mechanism is recently employed widely because it can be reduced in size in comparison with the linear type. For the convenience of explanation, the rotary type head positioning mechanism is hereinafter described as a rotary actuator.
FIG. 1 is a sectional view of schematic structure of a magnetic disk storage apparatus providing a conventional ordinary rotary head positioning mechanism and FIG. 2 is a plan view of the essential portion thereof. In these figures, three magnetic disks 112, for example, are rotatably supported by a spindle 113 in the enclosure 111 and these disks 112 are rotated at a constant speed, for example, of 3600 rpm by a spindle motor 114. The magnetic heads 115 are coupled with head arms 117 through suspension springs 116 and are positioned to the designated tracks of the magnetic disks 112 by the rotary actuator.
The rotary actuator is composed of a rotary member 118 which fixes head arms 117 and is rotatably supported by the enclosure 111 and a positioning motor, for example, a voice coil motor 119 for rotating such member 118 to rotate magnetic heads 115 through a specified angle about the rotating axis of the rotating member 118. This actuator also takes balance between the head arm side and motor side by setting the gravity center to the rotating axis of the rotating member 118 to eliminate positioning error for vibration input in the translational direction.
Moreover, in a magnetic disk storage apparatus for realizing high recording density, a closed loop servo control means is employed for controlling positioning of the actuator. This closed loop servo control means discriminates the current position of a magnetic head from the original point by reading servo information on the magnetic disk with the magnetic head, also computes distance up to the designated track position from the current position and drives the positioning motor based on the result of computation to position the magnetic head at the designated track.
In such a magnetic disk storage apparatus providing such a rotary actuator, positioning error may be generated easily by rotary movement (motion) generated by external vibration or impact. Namely, when vibration in the translational direction within the plane perpendicular to the rotating axis of the disk is applied, a rotating movement component is generated on the enclosure. In this case, a rotating force is not applied and only translational force is applied in the balanced actuator, namely a movement different from that of the enclosure is carried out in the actuator. Therefore, the relative positions of the disk and the head deviate, generating a positioning error. Even in an unbalanced actuator, such a positioning error is also generated.
In the prior art, it has been considered to make large such servo gain in order to reduce such positioning error but it has a limitation and it is generally attempted to employ the structure to attenuate external vibration or impact by making large an attenuation ratio by loading vibration proof members between the enclosure 111 and the frame. Namely, the conventional apparatus has employed a structure that vibration proof members having spring constant are allocated at the side or bottom plane of the enclosure to support the enclosure with the frame.
Such vibration proof structure has been effective within the practical range for a large size magnetic disk storage apparatus but has been insufficient for a recent small size and large capacity magnetic disk storage apparatus. Namely, in the small size and large capacity disk storage apparatus, the track pitch is very narrow to realize high recording density, the apparatus easily receives vibration or impact because it is mounted to a small size computer such as lap top type apparatus and moreover the apparatus vibrates largely for small vibration input because it is also designed in light weight. Accordingly, the relative position of disk and head is easily deviated for vibration input in the translational direction and thereby head positioning error is easily generated.